Radiomics on 177Lu-DOTATATE Posttreatment Scans: Feasibility, Preprocessing Optimization, and Planar-SPECT Comparison.

The landscape of treatment options in neuroendocrine tumors (NET) has changed in the last 5 years. Novel targeted drugs have been introduced and approved for distinct types of NET. Furthermore, with the first randomized trial on ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) in midgut NET, not only is approval of this treatment awaited but also its more widespread use. Techniques and choices of radionuclides have changed over time as well as imaging tools. Recognition of well-differentiated NET G3 within the group of neuroendocrine neoplasms G3 has widened the spectrum of chemotherapeutic drugs used in this field. Even more so, it has become important to provide recommendations for daily clinical practice on how to safely use novel drugs, chemotherapeutic agents, and PRRT. The updated ENETS consensus guidelines for the standards of care in NET provide a tool to accurately assess the diagnosis of NET as well as practical recommendations for the use of surgery, and the different systemic therapeutic options that are available for the management of NET.

Background: Peptide receptor radionuclide therapy (PRRT) is a validated treatment for somatostatin receptor overexpressing neuroendocrine tumors (NETs). The NETTER-1 trial demonstrated a pronounced positive effect on progression-free-survival compared to high dose somatostatin analogs (SSAs), with a strong tendency toward overall survival benefit. Our aim was to investigate the influence of pretreatment with everolimus and/or sunitinib on subacute hematotoxicity of PRRT. To assess the influence of prior treatment with everolimus/sunitinib might be of clinical relevance due to the link between short-term hematotoxicity and increased incidence of late hematotoxicity.Material and methods: Our single-center retrospective study enrolled all patients treated with 177Lu-DOTATATE PRRT (1–4 cycles of 7.4 GBq), between November 2013 and July 2018. Patients were assigned to two groups according to their pretreatment: no targeted agents (N = 41), or targeted agents (everolimus, sunitinib or both; N = 41). The end point was subacute hematotoxicity, defined as the nadir value between the first administration until 3 months after the last administration, using the CTCAE 4.03 classification. The impact of splenectomy was also explored.Results: Eighty percent of patients had a primary gastroenteropancreatic NET. No statistically significant differences in severe subacute hematotoxicity were seen in the pretreated group vs. the naive group for hemoglobin (grade 3/4: 12% vs. 22%), neither for leucocytes (grade 3/4: 10% vs. 7%), neutrophils (grade 3/4: 5% vs. 7%), lymphocytes (grade 3/4: 49% vs. 37%) and platelets (grade 3/4: 15% vs. 15%). Furthermore, we observed significantly lower toxicity for total white blood cells, lymphocytes and platelets in the subgroup that had splenectomy (N = 12). Limitations of this study include the potential bias in lack of use of targeted agents in patients more susceptible to toxicity, and the limited number of patients and events.Conclusions: In a patient cohort with NET pretreated with everolimus and/or sunitinib, we could not demonstrate a significant effect of prior/pretreatment with everolimus and/or sunitinib on the subacute hematotoxicity of 177Lu-DOTATATE PRRT.

PurposeThis study aimed to investigate the role of pre-treatment neutrophil-to-lymphocyte ratio (NLR) and monocyte-to-lymphocyte ratio (MLR) in the prognosis assessment of 177Lu-DOTATATE Peptide Receptor Radionuclide Therapy (PRRT) treated patients with advanced metastatic neuroendocrine tumors (NETs).MethodsEligible PRRT-treated patients (n = 247, 2010–2019) were included. Pre-PRRT NLR and MLR were calculated from complete blood count data. Data on tumor characteristics, response to PRRT, progression-free survival (PFS), and overall survival (OS) were evaluated using COXPH analyses.ResultsIn NET patients, median values of NLR and MLR were 2.21 (IQR = 1.66–3.00) and 0.14 (IQR = 0.06–0.24), respectively. NLR showed significant positive association with G3 tumors (median = 3.64, IQR = 2.1–4.26, p = 0.022) and high 18F-FDG avidity (SUVmax>5) (median = 2.5, IQR = 1.82–3.56, p = 0.003). MLR was significantly associated with high disease burden (median = 0.18, IQR = 0.08–0.29, p = 0.0083). MLR distinguished between the PRRT non-responders with progressive disease and responders with complete/partial response (median 0.19 versus 0.12, p = 0.043) or responders with stable disease (median 0.19 versus 0.14, p = 0.045). The ratios independently correlated with disease progression and OS. Patients in NLRhigh (>3.5) group displayed significantly shorter median PFS and OS (48 and 58 months) compared to NLRlow (≤3.5) group (108 and 96 months) (p < 0.01). Patients in MLRhigh (>0.25) group displayed significantly shorter median PFS and OS (40 and 52 months) compared to MLRlow (≤0.25) group (108 and 102 months) (p < 0.01).ConclusionPre-treatment NLR and MLR had an independent prognostic impact on disease progression and OS in PRRT-treated NET patients. This routine, inexpensive CBC-based test in the standard pre-PRRT workup demonstrates the prognostic value and may aid clinicians in the risk stratification of NET patients.

623 Background: Neuroendocrine tumors (NETs) are rare but increasing in incidence. The only curative treatment is surgery, which in many cases is not an option due to metastatic disease at diagnosis. The NETTER-1 study showed high efficacy and low toxicity of peptide receptor radionuclide therapy (PRRT) for midgut NETs. Here, we present our initial experience with PRRT in the treatment of patients with NET. Methods: Fifty-two patients (27 males and 25 females; 37 - 81 yo, mean ± SD: 61.8 ± 10.6 years) with documented progressive NET (25 pancreas, 17 small intestine, 1 coecum, 4 unknown primary, 3 paragangliomas, and 2 pheochromocytomas) were referred to undergo PRRT at our institution from July 2018 to September 2019. Laboratory tests were obtained at baseline, 1 week before each cycle and every 3 months following treatment. Progression-free survival (PFS), objective response rate (ORR) and toxicity were assessed. An interim overall survival (OS) analysis was performed. Results, when possible, were compared with the NETTER-1 trial. Lines of therapy were documented. Results: 22/52 (42%) patients completed all 4 cycles of PRRT. 18/52 (34%) patients are currently being treated. 12/52 (23%) patients had to discontinue treatment. Hematotoxicity was the only side effect which can be related to PRRT. The 6-month and 9-month PFS rate was 82.4% and 66.8% respectively vs. 89% and 84% in the NETTER-1 trial. The ORR was 36% vs. 18% in the NETTER-1 trial. In the interim OS analysis, 6 deaths occurred. In contrast to the NETTER-1 study, PRRT in our patient cohort was performed later in the course of treatment (median lines of therapy before PRRT = 4 ±1.3 (range 1-6)). Conclusions: Our preliminary data show overall good results of PRRT in patients with NETs. However, compared to the NETTER-1 trial, PFS is shorter which is most likely due to the extensive pretreatment, but ORR was higher. [Table: see text]

BackgroundNeuroendocrine tumors have increased in prevalence and diversity in recent years and are often diagnosed at metastatic stages. Compared with nonradioactive systemic treatment with somatostatin analogs, peptide receptor radionuclide therapy (PRRT) has shown superior overall survival benefits for well-differentiated neuroendocrine tumor patients. This study aimed to identify biomarkers from 68Ga‒DOTATOC PET/CT scans to predict survival in patients treated with PRRT in the clinic.MethodologyThis retrospective study analyzed 68Ga-DOTATOC PET/CT data from 67 NET patients undergoing PRRT. Tumor volumes and SUV metrics were segmented using standardized protocols. Radiomics features from liver metastases were extracted and preprocessed for analysis. Data were analysed via Kaplan-Meier, Cox regression, and PCA to evaluate the prognostic value of volumetric-, radiomics-, and clinicopathological parameters.ResultsThis study included scans from 67 patients with an average age of 67 years. The mean survival time was 46.5 months, with 43% of patients alive or lost to follow-up at the conclusion of data collection. Despite comprehensive analyses, neither volumetric parameters, including total tumor volume and organ-specific tumor volume, nor SUV values (SUVmax and SUVmean) were robust predictors of overall survival. K‒M and Cox regression analyses revealed no significant differences in survival between the high- and low-risk groups for these parameters. Furthermore, radiomics features extracted from liver metastases did not demonstrate significant prognostic value.ConclusionQuantification of 68Ga-DOTATOC PET/CT-derived parameters offers limited prognostic value for OS in NET patients who are receiving PRRT in clinical practice. These findings might emphasize the current robust integration of imaging in clinical decision-making for NET management.

Peptide receptor radionuclide therapy (PRRT) is approved in the US for treatment of gastroenteropancreatic neuroendocrine tumors (NETs), but data on PRRT outcomes within US populations remain scarce. To analyze the first 2 years of PRRT implementation at a US-based NET referral center. This cohort study was conducted using medical records of patients with metastatic NET receiving PRRT from 2018 through 2020 in a NET program at a tertiary referral center. Included patients were those at the center with metastatic NETs who received at least 1 dose of PRRT over the study period. Laboratory toxic effects were assessed using Common Terminology Criteria for Adverse Events version 5.0. Tumor response was determined using Response Evaluation Criteria in Solid Tumors 1.1. Survival analysis was conducted to identify factors associated with progression-free survival (PFS) and overall survival. Data were analyzed from August 2018 through August 2020. Receiving 4 cycles of lutetium-177-dotatate infusion, separated by 8-week intervals targeted to 7.4 GBq (200 mCi) per dose. Data were compared from before and after PRRT to determine hematologic, liver, and kidney toxic effects and to assess tumor progression and patient survival. Among 78 patients receiving at least 1 dose of PRRT, median (interquartile range) age at PRRT initiation was 59.8 (53.5-69.2) years and 39 (50.0%) were men. The most common primary NET sites included small bowel, occurring in 34 patients (43.6%), and pancreas, occurring in 22 patients (28.2%). World Health Organization grade 1 or 2 tumors occurred in 62 patients (79.5%). Among all patients, 56 patients underwent pretreatment with tumor resection (71.8%), 49 patients received nonsomatostatin analogue systemic therapy (62.8%), and 49 patients received liver-directed therapy (62.8%). At least 1 grade 2 or greater toxic effect was found in 47 patients (60.3%). Median PFS was 21.6 months for the study group, was not reached by 22 months for patients with small bowel primary tumors, and was 13.3 months for patients with pancreatic primary tumors. Having a small bowel primary tumor was associated with a lower rate of progression compared with having a pancreatic primary tumor (hazard ratio, 0.19; 95% CI, 0.07-0.55; P = .01). Median overall survival was not reached. This cohort study of patients with metastatic NETs found that PRRT was associated with laboratory-measured toxic effects during treatment for most patients and an overall median PFS of 21.6 months. Patients with small bowel NETs had longer PFS after PRRT compared with patients with pancreatic NETs.

IntroductionPrimary cardiac paragangliomas are rare tumors. Metastatic disease is even rarer. Surgical management is technically challenging, and sometimes even impossible. Available therapeutic modalities for metastatic disease include external beam radiation therapy as well as systemic treatments, namely 131I-MIBG and more recently, peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE. To our knowledge, this is the first case of progressive unresectable cardiac paraganglioma with intracardiac extension treated with dosimetry based personalized PRRT to be reported. This case is of particular interest since it documents for the first time the efficacy, and especially the safety of the 177Lu-DOTATATE PRRT in this precarious context for which therapeutic options are limited.Case PresentationA 47-year-old man with no medical history consulted for rapidly decreasing exercise tolerance. The investigation demonstrated an unresectable progressing metastatic cardiac paraganglioma with intracardiac extension. The patient was treated with personalized 177Lu-DOTATATE PRRT and showed complete symptomatic and partial anatomical responses, with a progression-free survival of 13 months.ConclusionsPRRT with 177Lu-DOTATATE should be considered for inoperable cardiac paraganglioma. No major hemodynamic complications were experienced. Therapy resulted in safety and substantially improved quality of life.

Neuroendocrine tumours may originate from the lungs, thymus, stomach, gastrointestinal tract and endocrine pancreas. A majority of the tumours are malignant. Metastases occur to regional and distal lymph nodes, liver, bones, lungs, mammary glands, subcutaneous tissue, central nervous system and adrenal glands. Although most neuroendocrine tumours are relatively slowly growing, poorly differentiated neuroendocrine carcinomas are fast growing neoplasms with high proliferative activity. A characteristic feature of many neuroendocrine tumours is the ability to produce and secrete various hormones and peptides, leading to endocrine symptoms that can be very disabling and cause substantial morbidity. Small bowel carcinoids, for example, produce serotonin giving rise to the classical carcinoid syndrome with flushing, diarrhea, right-sided heart disease and asthma. A prerequisite for the carcinoid syndrome to occur is usually the presence of liver metastases. Lung carcinoids rarely produce serotonin, but may instead secrete histamine causing an atypical carcinoid syndrome with generalized flushing, diarrhea, periorbital oedema, lacrimation and asthma. They may also produce adrenocorticotropic hormone or corticotropin-releasing factor, resulting in an ectopic Cushing's syndrome. Endocrine pancreatic tumours may as well secrete various hormones, such as gastrin, insulin, glucagon, vasoactive intestinal polypeptide (VIP) or somatostatin, resulting in the corresponding syndrome. The treatment of patients with metastatic neuroendocrine tumours is based on primary tumour origin, tumour biology, stage and grade and includes debulking by surgery, liver embolization with particles, chemoembolization, radioembolization, radiofrequency ablation and peptide receptor radionuclide therapy (PRRT) with 90Yttrium-DOTATOC or 177Lutetium-DOTATATE. Medical treatment consists of biotherapy with alpha-interferon and somatostatin analogues, various chemotherapy regimens, angiogenesis inhibitors, tyrosine kinase inhibitors and mTOR inhibitors. In this special issue in the International Journal of Hepatology, focus is on the various specific treatment possibilities for patients with neuroendocrine tumours metastatic to the liver. There are two papers describing the role of surgery in these patients, and one clinical study reporting the results of liver transplantation. Surgical debulking should always be considered, and liver transplantation may in selected cases be an option. Because of the immunosuppression, it is however of utmost importance that every effort is made to exclude remaining tumour outside the liver before transplantation. Three papers deals with hepatic arterial embolization, one of them reviews the role of hepatic arterial embolization for debulking of liver metastases. Another paper is about a clinical study and a review of radioembolization, which is a promising alternative for this patient group with possible long-lasting effect and few serious adverse effects. An important disadvantage (also with particle and chemoembolization) is that most patients with neuroendocrine tumours metastatic to the liver in addition have spread of the tumour to lymph nodes and/or other distant organs such as the bones, necessitating systemic therapy. In patients with normal bone marrow and renal function, PRRT is thus often preferred to radioembolization, which however may be considered if the patient shows progression later after PRRT. A randomized clinical trial comparing the various embolization methods, particle embolization, chemoembolization and radioembolization, would nevertheless be highly desirable. Three papers review the possible systemic therapies for patients with liver metastases from neuroendocrine tumours. This year, two new drugs have been approved for treatment of patients with metastatic endocrine pancreatic tumours, everolimus and sunitinib. This represents an important progress in the therapeutic arsenal for patients with neuroendocrine tumours. There is however still a need for more new drugs, and especially for patients with midgut carcinoids, in whom the therapeutic options are limited after progression. In addition, there is an urgent need to learn how to use, combine and sequence the various therapeutic alternatives, including chemotherapy, biotherapy, newer drugs and PRRT. Dan Granberg Wouter de Herder Dermot O'Toole Larry Kvols

IntroductionWell-differentiated metastatic functioning neuroendocrine tumors (NETs), particularly of gastrointestinal origin, pose diagnostic and therapeutic challenges. Although often slow growing, they may follow an unpredictable course. Somatostatin analogues (SSAs) are the first-line therapy, while peptide receptor radionuclide therapy (PRRT) with Lu-177-DOTATATE has become an established second-line option in progressive disease. Here, we present a case of functioning NET with liver, mesenteric and bone involvement, showing favorable long-term response to initial PRRT and later re-treatment upon biochemical progression.Clinical CaseA 2019 initial evaluation revealed multiple hepatic metastases, mesenteric nodules and bone lesions. Octreoscan confirmed somatostatin receptor expression. Diagnosis: functioning NET, likely gastrointestinal origin, stage IV. The patient was started on lanreotide 120 mg/month. In 2020, PET-Ga68 demonstrated progressive disease; liver biopsy confirmed well-differentiated G1 NET (low Ki-67). The NET tumor board recommended PRRT with Lu-177-DOTATATE. Post-therapy follow-up showed biochemical improvement and radiologic stabilization. PET-Ga68 in 2022 and CT in 2023 confirmed partial tumor shrinkage with stable disease.In April 2024, PET-Ga68 revealed persistent somatostatin-avid metastases with minor radiologic progression. Despite this, the patient remained asymptomatic, with preserved renal and bone marrow functions. In early 2025, the multidisciplinary team proposed PRRT re-treatment due to favorable profile: G1 tumor, strong receptor expression, no clinical deterioration and a progression-free interval >3 years. A dosimetric evaluation was performed, and a new Lu-177 cycle was scheduled. This decision was supported by international guidance and by increasing real-world experience suggesting that PRRT re-treatment may be a safe and effective option in selected patients.ConclusionThis case underscores the importance of multidisciplinary management in advanced NETs and highlights the potential of PRRT not only in initial treatment but also as re-treatment in selected patients. Key criteria for re-treatment include sustained receptor expression, clinical stability, organ function preservation, and significant time since first PRRT. Re-treatment with Lu-177 should be considered a valuable tool in the therapeutic arsenal for NETs, especially when tumor biology and patient profile remain favorable over time. This case also illustrates the relevance of integrating functional imaging and dosimetric evaluation into personalized decision-making pathways. Individualized assessment and adherence to updated guidelines are essential for optimizing outcomes.

Peptide receptor radionuclide therapy (PRRT) is an established treatment for patients with well-differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NETs) expressing somatostatin receptors (SSTR). Despite robust trial and real-world data, heterogeneity persists regarding patient selection, therapeutic sequencing, and follow-up strategies. A Delphi consensus was conducted by the Galician Multidisciplinary Group on Neuroendocrine and Endocrine Tumors (GGNET). Ten experts in oncology, endocrinology, nuclear medicine, and radiology participated. 29 clinical statements were developed after a systematic review and rated using a 4-point Likert scale. Consensus was defined as ≥ 70% agreement. Consensus (defined a priori as ≥ 70% agreement) was achieved for all statements although the level of agreement varied across domains. PRRT was endorsed for patients with unresectable or metastatic, progressive, well-differentiated GEP-NETs (grades 1-3, Ki-67 ≤ 55%) with confirmed SSTR expression. SSTR-targeted imaging (PET or scintigraphy) was considered mandatory for eligibility, with PET identified as the preferred modality. [18F]-FDG-PET was recommended selectively as a complementary prognostic tool in higher-grade tumors, rapid progression, or discordant imaging. Multidisciplinary tumor board review was universally supported. Guidance was provided on treatment administration, including standard dosing, renal protection, hematologic monitoring, and individualized risk assessment. Routine interim imaging was not recommended. Structured follow-up with CT/MRI was endorsed, with indication-driven use of SSTR or FDG-PET and limited routine value of non-specific biomarkers. Functional biomarkers, such as 5-HIAA and peptide hormones, retained utility in functioning tumors. This Delphi consensus provides pragmatic, multidisciplinary, and evidence-informed guidance to harmonize routine clinical practice in the use of PRRT for well-differentiated, SSTR-positive NETs. The proposed statements and the algorithm aim to harmonize practice across centers, reduce variability in care, enhance safety, and ultimately improve patient outcomes.

Peptide receptor radionuclide therapy is an effective treatment option for patients with well-differentiated somatostatin receptor-expressing neuroendocrine tumors. However, published data result mainly from retrospective monocentric studies. We initiated a multi-institutional, prospective, board-reviewed registry for patients treated with peptide receptor radionuclide therapy in Germany in 2009. In five centers, 297 patients were registered. Primary tumors were mainly derived from pancreas (117/297) and small intestine (80/297), whereas 56 were of unknown primary. Most tumors were well differentiated with median Ki67 proliferation rate of 5% (range 0.9-70%). Peptide receptor radionuclide therapy was performed using mainly yttrium-90 and/or lutetium-177 as radionuclides in 1-8 cycles. Mean overall survival was estimated at 213 months with follow-up between 1 and 230 months after initial diagnosis, and 87 months with follow-up between 1 and 92 months after start of peptide receptor radionuclide therapy. Median overall survival was not yet reached. Subgroup analysis demonstrated that best results were obtained in neuroendocrine tumors with proliferation rate below 20%. Our results indicate that peptide receptor radionuclide therapy is an effective treatment for well- and moderately differentiated neuroendocrine tumors irrespective of previous therapies and should be regarded as one of the primary treatment options for patients with somatostatin receptor-expressing neuroendocrine tumors.

Aim: Limited therapeutic options have highlighted the demand for new treatment modalities for patients with advanced neuroendocrine tumors (NET). Promising results of initial studies have warranted the implementation of peptide receptor radionuclide therapy (PRRT) in clinical practice. However, this treatment option still needs clinical evaluation. Methods: In this study, we evaluated the PRRT treatment response of 69 Danish patients with NET mainly originating from the gastroenteropancreatic system. Fifty-six patients (81%) were referred for PRRT to the Department of Nuclear Medicine, University Hospital Basel, Switzerland, between 2004 and 2008 due to progression assessed by the referring physicians. However, when retrospectively evaluated, only 42 of the 69 patients (61%) had progression according to RECIST (Response Evaluation Criteria in Solid Tumors). Most patients were treated with ⁹⁰Y-DOTATOC. Results: Based on RECIST, a complete response was observed in 5 patients (7.4%), a partial response in 11 patients (16.2%) and stable disease in 42 patients (61.8%). Progressive disease after completed therapy was observed in 10 patients (14.7%). The median progression-free survival was 29 months (95% CI: 22–36 months). Pancreatic NET seemed to respond better to PRRT than small intestinal carcinoid tumors (p = 0.03). The overall frequency of serious adverse events was low. Conclusion: Implementation of PRRT in clinical routine has provided a valuable new therapeutic option for the treatment of advanced NET. We suggest that PRRT may advance from second- or third-line to first- or second-line therapy in inoperable/unresectable NET patients.

The objective of this retrospective study was to determine the role of 18F-FDG PET/CT in a large cohort of 495 patients with metastatic neuroendocrine neoplasms (NENs) who were treated with peptide receptor radionuclide therapy (PRRT) with a long-term follow-up. Methods: The 495 patients were treated with 177Lu- or 90Y-DOTATOC/DOTATATE PRRT between February 2002 and July 2018. All subjects received both 68Ga-DOTATOC/TATE/NOC and 18F-FDG PET/CT before treatment and were followed 3-189 mo. Kaplan-Meier analysis, log-rank testing (Mantel-Cox), and Cox regression analysis were performed for overall survival (OS) and progression-free survival (PFS). Results: One hundred ninety-nine patients (40.2%) presented with pancreatic NENs, 49 with cancer of unknown primary, and 139 with midgut NENs, whereas the primary tumor was present in the rectum in 20, in the lung in 38, in the stomach in 8, and in other locations in 42. 18F-FDG PET/CT was positive in 382 (77.2%) patients and negative in 113 (22.8%) before PRRT, whereas 100% were 68Ga-DOTATOC/TATE/NOC-positive. For all patients, the median PFS and OS, defined from the start of PRRT, were 19.6 mo and 58.7 mo, respectively. Positive 18F-FDG results predicted shorter PFS (18.5 mo vs. 24.1 mo; P = 0.0015) and OS (53.2 mo vs. 83.1 mo; P < 0.001) than negative 18F-FDG results. Among the cases of pancreatic NENs, the median OS was 52.8 mo in 18F-FDG-positive subjects and 114.3 mo in 18F-FDG-negative subjects (P = 0.0006). For all patients positive for 18F-FDG uptake, and a ratio of more than 2 for the highest SUVmax on 68Ga-somatostatin receptor (SSTR) PET to the most 18F-FDG-avid tumor lesions, the median OS was 53.0 mo, compared with 43.4 mo in those patients with a ratio of less than 2 (P = 0.030). For patients with no 18F-FDG uptake (complete mismatch imaging pattern), the median OS was 108.3 mo versus 76.9 mo for an SUVmax of more than 15.0 and an SUVmax of 15.0 or less on 68Ga-SSTR PET/CT, respectively. Conclusion: The presence of positive lesions on 18F-FDG PET is an independent prognostic factor in patients with NENs treated with PRRT. Metabolic imaging with 18F-FDG PET/CT complements the molecular imaging aspect of 68Ga-SSTR PET/CT for the prognosis of survival after PRRT. High SSTR expression combined with negative 18F-FDG PET/CT results is associated with the most favorable long-term prognosis.

Preoperative knowledge of tumor consistency and the likelihood of gross total resection (GTR) would greatly benefit planning of pituitary adenoma surgery, however, no reliable methods currently exist. To evaluate the utility of radiomic analysis of MRI for predicting tumor consistency and GTR. To explore the interpretability of contributing radiomic features. Patients undergoing first endoscopic surgery for pituitary macroadenomas were included. Tumor consistency was assessed intraoperatively, GTR was assessed based on postoperative MRI. Radiomic features were extracted from axial T2-weighted MRI. Low-variability and highly intercorrelated features were removed. Random Forest Classifiers were optimized using 70 % of patient data and evaluated on the remaining 30 %. Relative feature importance was assessed using the Gini-Simpson index. 542 patients were included. GTR was achieved in 325 (60.0 %) cases, firm tumors were encountered in 122 (22.5 %) cases. There was a significant correlation between GTR and tumor consistency (67.1 % vs. 35.2 %, p<0.001). 1688 radiomic variables were extracted, 442 were removed due to low variance and 699 due to high intercorrelation. The consistency prediction model achieved an accuracy of 81.6 % and utilized 32 features, GTR prediction model achieved 79.1 % accuracy using 73 features. Radiomic analysis demonstrated significant potential for preoperative evaluation of pituitary adenomas. Texture and intensity-based features were the primary contributors to consistency prediction. However, the explanation of these features was insufficient. GTR prediction was predominantly driven by shape-related features. Our findings highlight the challenges of linking radiomic features to underlying tissue properties and emphasize the need for cautious interpretation.

81 Background: In metastatic neuroendocrine tumors (NET) peptide receptor radionuclide therapy (PRRT) using radiolabeled somatostatin analogues (Lu-177-DOTATATE) and selective intra-arterial radio-therapy (SIRT) with Y-90-microspheres are increasingly used promising treatment options. Rarely patients have been treated with sequential use of both treatment modalities . Severe adverse effects are rare and mainly concern hematologic changes and development of prolonged cytopenias . There is no data about possible cumulative side effects particularly regarding hematologic toxicity in the case of sequential use of both treatments. Methods: 5 Patients with hepatic metastasized NET treated both with SIRT and PRRT during 2010 - 2019 were included. Average time interval between treatment of y90 and PRRT was 2.5 years. All of them were treated with y90 before PRRT. Average treatment with Y90 was 3 doses. Results: In the follow up Platelets (159 to 89), leukocytes (7.5 to 3.7) and hemoglobin (13 to 11.6 ) decreased significantly, LFTs, bilirubin and creatinine did not change significantly. No severe toxicity (Grade 3 or 4) was experienced. 80 % of the patients showed decreasing blood counts after the therapies and was prolonged for average of 9 months. Conclusions: In metastatic neuroendocrine tumors (NET) sequential treatment with peptide receptor radionuclide therapy (PRRT) using radiolabeled somatostatin analogues (Lu-177-DOTATATE) after selective intra-arterial radio-therapy (SIRT) with Y-90-microspheres is possible and well tolerated except for hematological toxicity.